Minimally invasive ablative therapies, which include but are not limited to, Radio-Frequency Ablation (RFA), microwave thermal therapy and cryoablation, have been studied extensively over the past two decades for the treatment of a range of tumours, most notably in the kidney, lung and liver. These therapies are delivered by inserting a long thin needle-like device through a small incision in the skin. Imaging, which may typically be ultrasound or CT, may be used to guide the device to the tumour where the ablative energy is delivered. The goal is to heat (or freeze in the case of cryotherapy) the tumour to the point where cell kill is achieved, while minimizing damage to surrounding normal tissue. These therapies have demonstrated therapeutic effects and have the potential to reduce patient recuperation times and length of hospital stays when compared to surgical treatment, thereby reducing treatment costs.
Despite the advantages of minimally-invasive ablative therapies, they remain a secondary option, recommended only for patients who are not suitable for surgery, which is the current standard of care for many tumours. For example, both the American Urological Association [1] and the European Association of Urology [2] recommend partial nephrectomy as the standard treatment for all T1 renal tumours. Minimally invasive ablative therapies are recommended only as an option in patients with small tumours and with health conditions that would increase the risks of surgery. The principal reason that surgery remains the standard is that minimally invasive ablation therapies have a significantly higher rate of local tumour recurrence than surgical approaches (10-13% vs. 1-2%) [1], with large tumours often recurring at the periphery of the ablation zone. In order for minimally invasive ablative therapies to become the standard of care they must demonstrate an ability to achieve tumour control that is equivalent to surgery.
Small coagulation volumes present another barrier to widespread adoption of minimally invasive ablation therapies. Typically, ablation is recommended only for tumours smaller than 3 cm. Studies have shown that as tumour size increases, both the success rate [3] and long-term disease-free survival rate [4] for minimally ablative therapies decrease. Furthermore, complication rates, which in most studies are around 10%, are also correlated with tumour size and location [5]. Complications can arise from injuries incurred in the placement of the ablative device or from thermal injury to critical normal structures. Complication rates increase with tumour size and complexity because these cases conventionally require multiple rounds of insertions and ablations and the risk of injury increases with each round of insertion and ablation. Finally, the success of these procedures shows a significant dependence on operator experience [6].